The present invention relates to a vertical and optical distortion correction apparatus in a projection television set, and more particularly, to a vertical and optical distortion correction apparatus in a projection television (TV) set for correcting vertical and optical distortions while reducing thermal loss of a convergence output end and facilitating color balance control.
An existing projection TV set includes three cathode ray tubes (CRTs) for converting an electrical image signal into red, green and blue light. These CRTs have a size of seven to nine inches. The CRT for red light and the CRT for blue light are disposed to the left and right sides with respect to the CRT for green light, respectively. Each CRT includes a deflection yoke portion for deflecting an electrical beam horizontally and vertically. Thus, in case of a blue image displayed on a screen by the blue light CRT, an optical distortion due to arrangement of the three CRTs is shown in the upperleft end and lowerleft end of the image as shown in FIG. 3A, and distortion due to a deflection yoke portion (hereinafter, referred to as a "vertical distortion") is shown in the upperright end and the lowerright end of the image. In case of a green image displayed by the green light CRT, a vertical distortion of the image shows up strongly in the center-top and the center-bottom of the image as shown in FIG. 3B. In case of a red image displayed by the red light CRT, a vertical distortion of the image shows up strongly in the upperleft and the lowerleft end as shown in FIG. 3C and an optical distortion of the image shows up strongly in the upperright end and the lowerright end as shown in FIG. 3C. A digital convergence correction circuit and an analog convergence correction circuit are usually used for correcting the vertical distortion and optical distortion. These correction circuits produce voltage waveforms for correcting distortions of the red, green and blue images, and the produced voltage waveforms are supplied to convergence amplifier circuits of the red, green and blue CRTs, respectively. That is, the produced voltage waveforms are applied to a convergence yoke portion of each CRT. Each convergence yoke portion corrects the distortions according to the applied voltage waveform.
However, since heat proportional to a degree of correcting the convergence is generated in CRTs, in the case of the conventional distortion correction, a large thermal energy loss is generated. Such a problem shortens the life of the apparatus and negatively impacts the reliability of the apparatus.